Among the benefits of miniaturization in the electronics and the optics industries is the ability to integrate into a single unit two or more capabilities which were previously considered unrelated. An example is the cellular telephone camera having both wireless transmission capability and image capture capability. Images may be stored or may be transmitted using the same circuitry and antenna used for transmitting voice information.
In a cellular phone camera, the approaches to providing focus vary significantly with respect to complexity. For minimal complexity, a focus lens may be fixed in position. The fixed position may be a close focus mode (macro focus), if it is assumed that the unit will be used primarily for close range photography. As another possibility, the fixed position may be one that provides a compromise between enabling high resolution close-ups and enabling high resolution distance imaging. Alternatively, the fixed position may be a compromise within the range from providing optimal focus for nearby objects to providing optimal focus for distant objects.
A focusing approach that involves a much greater degree of complexity is one which incorporates the auto focusing systems of high-end digital cameras into the cellular telephone camera. Such systems may mount a focus lens onto a drive mechanism capable of changing the distance between the lens and an image sensor. The drive mechanism may be manipulated by a motor which is controlled on the basis of information from a range finder. Range finders receive light through the focus lens and determine the distance between the image plane of the lens and the plane of the sensor. One range finding technique is known as “phase difference detection.” A controller receives the distance information from the range finder and activates the motor to move the lens the proper distance to place the image plane of the lens on the sensor. Unfortunately, such a system may add significantly to the cost of the cellular telephone.
A less complex approach that allows multiple focus positions is one that enables manual movement of a focus lens. For example, the user may selectively change from a position for optimal focus for distant objects and optimal position for nearby objects merely by maneuvering a lever or by rotating a focus-setting member.
While the various approaches function well for their intended purpose, each approach has its drawbacks.